That could be a hard one as Mozilla really makes it difficult to integrate with the existing themes.
But I maybe found something that is worth trying. Can you create a GitHub issue for this?

You have to access the icon using the "Extensions" button on the toolbar (puzzle piece icon). In its menu you'll find "Undo Close Tab" and if you like, you can select "Pin to Toolbar" from the menu there.

This is not at all convenient but this is the way Mozilla enforces for Add-ons.

Thanks for all those suggestions, but they would have been better placed on GitHub as discussion on each individual one would have been possible.

- Timestamps: Most users don't care about this and a "timestamp" actually consumes A LOT of space (it's not just the time but the date somehow has to fit, too).
- More than 25 items is not possible. Please read my point about this on my Add-on description. This is something Mozilla has to fix.
- Adjustable char limit is difficult as texts are variable width and I won't go into the rabbit hole of "char width calculation". Most users want to see "as much as possible" anyway.
- Option for multiple tabs is not possible with Mozilla API. You'll have to open the menu multiple times to get this. I'm limited to what Mozilla allows to Add-ons.
- Default for tab-bar context menu to "ON" is a good idea. I'll put that on my list for the next update.
- The icon won't change. Sorry but it has been refined several times and whatever you do you'll always have a few users that don't like it.
- The icon should be dark mode friendly at least on the toolbar. The icon in the context menu actually can not be changed. Mozilla only allows icons to be changed in sub menus and not on top level. And my default icon is the icon for light mode as that used to be the most used mode when the Add-on was created.